With the soil temperatures dropping, producers might be thinking about applying anhydrous ammonia to cropland. Ongoing drought conditions, however, may necessitate a change from typical practices, according to Texas AgriLife Extension Service and Texas AgriLife Research experts.
“Soils throughout the area are dry, and water is very important in providing proper soil physical conditions to ensure complete sealing of the ammonia fertilizer at the injection site,” said Dr. Brent Bean, AgriLife Extension agronomist in Amarillo.
In a joint recommendation with Dr. Paul DeLaune, AgriLife Research environmental soil scientist from Vernon, Bean said anhydrous ammonia can be applied after soil temperatures drop below 50 degrees.
“However, it may be a good idea this year to wait until late winter in hopes of getting enough moisture to improve soil conditions for better sealing of the fertilizer track,” Bean said. “If nature does not provide enough precipitation to improve soil conditions, it may be necessary to apply irrigation prior to fertilizer application.”
The experts explained that ammonia is made up of 82 percent nitrogen and 18 percent hydrogen. It is called anhydrous ammonia because it does not contain water. It is normally a gas but is in a liquid form when stored under pressure. As a liquid, it weighs approximately 5 pounds per gallon but that can vary with temperature.
Once released in the soil, anhydrous ammonia expands rapidly as a gas and has a very strong attraction to water, DeLaune said. It quickly reacts in water forming ammonium, which has a positive charge. This positive charge allows it to be adsorbed to the negatively charged organic matter and clay particles in the soil.
Soil water is necessary in order for the ammonia to be converted to ammonium and held or attached to clay or organic matter, he said. Even dry soil contains some water, although there is less in sandy soils.
The biggest problem with dry soil is getting a proper seal at the injection point, Bean said. When ammonia is injected into the soil, the area occupied is generally 3 to 4 inches around the injection point. In sandy soils this may be closer to 6 inches. If clods are present leaving large air voids, the ammonia may occupy a larger area and will tend to move toward the surface.
Bean said work done by Dr. John Sawyer, Iowa State soil fertility specialist, shows that use of wing sealers immediately above the outlet port on the knife will help reduce the size of the retention zone and reduce the vertical movement of the ammonia. Sawyer also suggests closing disks to reduce ammonia loss by covering the injection track with soil.
Place ammonia deeper
Because ammonia will tend to move more in dry soil, anhydrous ammonia should likely be injected deeper than normal, DeLaune said. When injecting into dry soil, try to place the anhydrous ammonia at least 8 inches deep.
“Keep in mind that in a clay loam soil, it will require about 1 inch of water to wet the soil profile to a depth of 6 inches,” Bean said. “It should also be noted that excess moisture can prevent the sealing of injection knife openings.
“When injecting anhydrous ammonia, your nose is the best indicator that the ammonia is not being properly held in the soil,” he said. “After making one round in the field, check to see if you can still smell any ammonia. If so, then the equipment may need to be adjusted or the application may have to be delayed until better soil conditions are present.”
He did add, though, that the white ‘smoke’ that is sometimes seen at the time of application is water vapor and not ammonia.